Method of making alkylene glycols

ABSTRACT

Methods and systems for preparing alkylene glycols are described herein. The methods and systems incorporate the novel use of a high shear device to promote dispersion and solubility of alkylene oxides with water. The high shear device may allow for lower reaction temperatures and pressures and may also reduce reaction time.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of U.S. patentapplication Ser. No. 13/028,100, filed Feb. 15, 2011, which is acontinuation application of U.S. patent application Ser. No. 12/335,272,filed Dec. 15, 2008, which is a divisional application of U.S. patentapplication Ser. No. 12/142,443, filed Jun. 19, 2008, which claims thebenefit under 35 U.S.C. §119(e) of U.S. Provisional Patent ApplicationNo. 60/946,484, filed Jun. 27, 2007. The disclosure of said applicationsis hereby incorporated herein by reference.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not Applicable.

BACKGROUND

1. Field of the Invention

This invention relates generally to the field of chemical reactions.More specifically, the invention relates to methods of making alkyleneglycols incorporating high shear mixing.

2. Background of the Invention

Ethylene glycol is used as antifreeze in cooling and heating systems, inhydraulic brake fluids, as an industrial humectant, as an ingredient ofelectrolytic condensers, as a solvent in the paint and plasticsindustries, in the formulations of printers' inks, stamp pad inks, andinks for ballpoint pens, as a softening agent for cellophane, and in thesynthesis of safety explosives, plasticizers, synthetic fibers(TERYLENE®, DACRON®), and synthetic waxes. Ethylene glycol is also usedto de-ice airport runways and aircraft. Plainly, ethylene glycol is anindustrially important compound with many applications.

Prior methods for hydrating alkylene oxides to the alkylene glycolsinclude the direct hydration reaction without benefit of catalyst andthe catalytic hydration of alkylene oxides using mineral acid catalysts.These mineral acid catalytic reactions are homogeneous thereby posing aproblem for the commercial production of glycols since the catalyst iscarried over into the product and must be separated. Present commercialprocesses use a noncatalytic hydration procedure which must use largeratios of water to alkylene oxide thereby presenting a problem ofseparation of the water from the finished product. This separationconsumes large amounts of energy which recently has been the cause ofmuch concern.

Recently, attempts have been made to discover a new catalyst for thehydration of alkylene oxides to the respective glycols. For example,other catalytic processes use tetramethyl ammonium iodide and tetraethylammonium bromide, or organic tertiary amines such as triethylamine andpyrridine. Despite a focus on the catalyst technology, little has beendone toward improving the mixing of the alkylene oxide with the waterphase to optimize the reaction.

Consequently, there is a need for accelerated methods for making alkylglycols by improving the mixing of ethylene oxide into the water phase.

SUMMARY

Methods and systems for preparing alkylene glycols are described herein.The methods and systems incorporate the novel use of a high shear deviceto promote dispersion and solubility of an alkylene oxide in water. Thehigh shear device may allow for lower reaction temperatures andpressures and may also reduce reaction time. Further advantages andaspects of the disclosed methods and system are described below.

In an embodiment, a method of making an alkylene glycol comprisesintroducing an alkylene oxide gas into a liquid water stream to form agas-liquid stream. The method further comprises flowing the gas-liquidstream through a high shear device so as to form a dispersion with gasbubbles having a mean diameter less than about 1 micron. In addition themethod comprises contacting the gas-liquid stream with a catalyst in areactor to hydrate the alkylene oxide and form the alkylene glycol.

In an embodiment, a system for making a alkylene glycol comprises atleast one high shear device configured to form a dispersion of analkylene oxide and water. The high shear device comprises a rotor and astator. The rotor and the stator are separated by a shear gap in therange of from about 0.02 mm to about 5 mm. The shear gap is a minimumdistance between the rotor and the stator. The high shear device iscapable of producing a tip speed of the at least one rotor of greaterthan about 23 m/s (4,500 ft/min) In addition, the system comprises apump configured for delivering a liquid stream comprising liquid phaseto the high shear device. The system also comprises a reactor forhydrating the alkylene oxide coupled to said high shear device. Thereactor is configured for receiving the dispersion from the high sheardevice.

The foregoing has outlined rather broadly the features and technicaladvantages of the present invention in order that the detaileddescription of the invention that follows may be better understood.Additional features and advantages of the invention will be describedhereinafter that form the subject of the claims of the invention. Itshould be appreciated by those skilled in the art that the conceptionand the specific embodiments disclosed may be readily utilized as abasis for modifying or designing other structures for carrying out thesame purposes of the present invention. It should also be realized bythose skilled in the art that such equivalent constructions do notdepart from the spirit and scope of the invention as set forth in theappended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

For a detailed description of the preferred embodiments of theinvention, reference will now be made to the accompanying drawings inwhich:

FIG. 1 is a process flow diagram of a process for the hydration of analkylene oxide with water in liquid phase, according to certainembodiments of the invention; and

FIG. 2 is a longitudinal cross-section view of a multi-stage high sheardevice, as employed in an embodiment of the system of FIG. 1.

NOTATION AND NOMENCLATURE

Certain terms are used throughout the following description and claimsto refer to particular system components. This document does not intendto distinguish between components that differ in name but not function.

In the following discussion and in the claims, the terms “including” and“comprising” are used in an open-ended fashion, and thus should beinterpreted to mean “including, but not limited to . . . ”.

DETAILED DESCRIPTION

The disclosed methods and systems for the hydration of alkylene oxidesemploy a high shear mechanical device to provide rapid contact andmixing of the alkylene oxide gas and water in a controlled environmentin the reactor/mixer device. The term “alkylene oxide gas” as usedherein includes both substantially pure alkylene oxides as well asgaseous mixtures containing alkylene oxides. In particular, embodimentsof the systems and methods may be used in the production of alkyleneglycols from the hydration of alkylene oxides. Preferably, the methodcomprises a heterogeneous phase reaction of liquid water with analkylene oxide gas. The high shear device reduces the mass transferlimitations on the reaction and thus increases the overall reactionrate.

Chemical reactions involving liquids, gases and solids rely on time,temperature, and pressure to define the rate of reactions. In caseswhere it is desirable to react two or more raw materials of differentphases (e.g. solid and liquid; liquid and gas; solid, liquid and gas),one of the limiting factors in controlling the rate of reaction involvesthe contact time of the reactants. In the case of heterogeneouslycatalyzed reactions there is the additional rate limiting factor ofhaving the reacted products removed from the surface of the catalyst toenable the catalyst to catalyze further reactants. Contact time for thereactants and/or catalyst is often controlled by mixing which providescontact with two or more reactants involved in a chemical reaction. Areactor assembly that comprises an external high shear device or mixeras described herein makes possible decreased mass transfer limitationsand thereby allows the reaction to more closely approach kineticlimitations. When reaction rates are accelerated, residence times may bedecreased, thereby increasing obtainable throughput. Product yield maybe increased as a result of the high shear system and process.Alternatively, if the product yield of an existing process isacceptable, decreasing the required residence time by incorporation ofsuitable high shear may allow for the use of lower temperatures and/orpressures than conventional processes.

System for Hydration Alkylene Oxides. A high shear alkylene oxidehydration system will now be described in relation to FIG. 1, which is aprocess flow diagram of an embodiment of a high shear system 100 for theproduction of alkylene glycols via the hydration of alkylene oxides. Thebasic components of a representative system include external high sheardevice (HSD) 140, vessel 110, and pump 105. As shown in FIG. 1, the highshear device may be located external to vessel/reactor 110. Each ofthese components is further described in more detail below. Line 121 isconnected to pump 105 for introducing an alkylene oxide reactant (e.g.,water). Line 112 connects pump 105 to HSD 140, and line 118 connects HSD140 to vessel 110. Line 122 is connected to line 113 for introducing analkylene oxide gas. Line 117 is connected to vessel 110 for removal ofunreacted alkylene oxides, and other reaction gases. Additionalcomponents or process steps may be incorporated between vessel 110 andHSD 140, or ahead of pump 105 or HSD 140, if desired.

High shear devices (HSD) such as a high shear, or high shear mill, aregenerally divided into classes based upon their ability to mix fluids.Mixing is the process of reducing the size of inhomogeneous species orparticles within the fluid. One metric for the degree or thoroughness ofmixing is the energy density per unit volume that the mixing devicegenerates to disrupt the fluid particles. The classes are distinguishedbased on delivered energy density. There are three classes of industrialmixers having sufficient energy density to consistently produce mixturesor emulsions with particle or bubble sizes in the range of 0 to 50microns. High shear mechanical devices include homogenizers as well ascolloid mills.

High shear devices (HSD) such as a high shear, or high shear mill, aregenerally divided into classes based upon their ability to mix fluids.Mixing is the process of reducing the size of inhomogeneous species orparticles within the fluid. One metric for the degree or thoroughness ofmixing is the energy density per unit volume that the mixing devicegenerates to disrupt the fluid particles. The classes are distinguishedbased on delivered energy density. There are three classes of industrialmixers having sufficient energy density to consistently produce mixturesor emulsions with particle or bubble sizes in the range of 0 to 50 μm.

Homogenization valve systems are typically classified as high energydevices. Fluid to be processed is pumped under very high pressurethrough a narrow-gap valve into a lower pressure environment. Thepressure gradients across the valve and the resulting turbulence andcavitations act to break-up any particles in the fluid. These valvesystems are most commonly used in milk homogenization and can yieldaverage particle size range from about 0.01 μm to about 1 μm. At theother end of the spectrum are high shear systems classified as lowenergy devices. These systems usually have paddles or fluid rotors thatturn at high speed in a reservoir of fluid to be processed, which inmany of the more common applications is a food product. These systemsare usually used when average particle, or bubble, sizes of greater than20 microns are acceptable in the processed fluid.

Between low energy—high shears and homogenization valve systems, interms of the mixing energy density delivered to the fluid, are colloidmills, which are classified as intermediate energy devices. The typicalcolloid mill configuration includes a conical or disk rotor that isseparated from a complementary, liquid-cooled stator by aclosely-controlled rotor-stator gap, which is maybe between 0.025 mm and10.0 mm. Rotors are usually driven by an electric motor through a directdrive or belt mechanism. Many colloid mills, with proper adjustment, canachieve average particle, or bubble, sizes of about 0.01 μm to about 25μm in the processed fluid. These capabilities render colloid millsappropriate for a variety of applications including colloid andoil/water-based emulsion processing such as that required for cosmetics,mayonnaise, silicone/silver amalgam formation, or roofing-tar mixing.

An approximation of energy input into the fluid (kW/L/min) can be madeby measuring the motor energy (kW) and fluid output (L/min). Inembodiments, the energy expenditure of a high shear device is greaterthan 1000 W/m³. In embodiments, the energy expenditure is in the rangeof from about 3000 W/m³ to about 7500 W/m³. The shear rate generated ina high shear device may be greater than 20,000 s⁻¹. In embodiments, theshear rate generated is in the range of from 20,000 s⁻¹ to 100,000 s⁻¹.

Tip speed is the velocity (m/sec) associated with the end of one or morerevolving elements that is transmitting energy to the reactants. Tipspeed, for a rotating element, is the circumferential distance traveledby the tip of the rotor per unit of time, and is generally defined bythe equation V (m/sec)=π·D·n, where V is the tip speed, D is thediameter of the rotor, in meters, and n is the rotational speed of therotor, in revolutions per second. Tip speed is thus a function of therotor diameter and the rotation rate. Also, tip speed may be calculatedby multiplying the circumferential distance transcribed by the rotortip, 2πR, where R is the radius of the rotor (meters, for example) timesthe frequency of revolution (for example revolutions (meters, forexample) times the frequency of revolution (for example revolutions perminute, rpm).

For colloid mills, typical tip speeds are in excess of 23 m/sec (4500ft/min) and can exceed 40 m/sec (7900 ft/min) For the purpose of thepresent disclosure the term ‘high shear’ refers to mechanicalrotor-stator devices, such as mills or mixers, that are capable of tipspeeds in excess of 5 m/sec (1000 ft/min) and require an externalmechanically driven power device to drive energy into the stream ofproducts to be reacted. A high shear device combines high tip speedswith a very small shear gap to produce significant friction on thematerial being processed. Accordingly, a local pressure in the range ofabout 1000 MPa (about 145,000 psi) to about 1050 MPa (152,300 psi) andelevated temperatures at the tip of the shear mixer are produced duringoperation. In certain embodiments, the local pressure is at least about1034 MPa (about 150,000 psi).

Referring now to FIG. 2, there is presented a schematic diagram of ahigh shear device 200. High shear device 200 comprises at least onerotor-stator combination. The rotor-stator combinations may also beknown as generators 220, 230, 240 or stages without limitation. The highshear device 200 comprises at least two generators, and most preferably,the high shear device comprises at least three generators.

The first generator 220 comprises rotor 222 and stator 227. The secondgenerator 230 comprises rotor 223, and stator 228; the third generatorcomprises rotor 224 and stator 229. For each generator 220, 230, 240 therotor is rotatably driven by input 250. The generators 220, 230, 240rotate about axis 260 in rotational direction 265. Stator 227 is fixablycoupled to the high shear device wall 255.

The generators include gaps between the rotor and the stator. The firstgenerator 220 comprises a first gap 225; the second generator 230comprises a second gap 235; and the third generator 240 comprises athird gap 245. The gaps 225, 235, 245 are between about 0.025 mm (0.01in) and 10.0 mm (0.4 in) wide. Alternatively, the process comprisesutilization of a high shear device 200 wherein the gaps 225, 235, 245are between about 0.5 mm (0.02 in) and about 2.5 mm (0.1 in). In certaininstances the gap is maintained at about 1.5 mm (0.06 in).Alternatively, the gaps 225, 235, 245 are different between generators220, 230, 240. In certain instances, the gap 225 for the first generator220 is greater than about the gap 235 for the second generator 230,which is greater than about the gap 245 for the third generator 240.

Additionally, the width of the gaps 225, 235, 245 may comprise a coarse,medium, fine, and super-fine characterization. Rotors 222, 223, and 224and stators 227, 228, and 229 may be toothed designs. Each generator maycomprise two or more sets of rotor-stator teeth, as known in the art.Rotors 222, 223, and 224 may comprise a number of rotor teethcircumferentially spaced about the circumference of each rotor. Stators227, 228, and 229 may comprise a number of stator teethcircumferentially spaced about the circumference of each stator. Therotor and the stator may be of any suitable size. In one embodiment, theinner diameter of the rotor is about 64 mm and the outer diameter of thestator is about 60 mm. In other embodiments, the inner diameter of therotor is about 11.8 cm and the outer diameter of the stator is about15.4 cm. In further embodiments, the rotor and stator may have alternatediameters in order to alter the tip speed and shear pressures. Incertain embodiments, each of three stages is operated with a super-finegenerator, comprising a gap of between about 0.025 mm and about 3 mm.When a feed stream 205 including solid particles is to be sent throughhigh shear device 200, the appropriate gap width is first selected foran appropriate reduction in particle size and increase in particlesurface area. In embodiments, this is beneficial for increasing catalystsurface area by shearing and dispersing the particles.

High shear device 200 is fed a reaction mixture comprising the feedstream 205. Feed stream 205 comprises an emulsion of the dispersiblephase and the continuous phase. Emulsion refers to a liquefied mixturethat contains two distinguishable substances (or phases) that will notreadily mix and dissolve together. Most emulsions have a continuousphase (or matrix), which holds therein discontinuous droplets, bubbles,and/or particles of the other phase or substance. Emulsions may behighly viscous, such as slurries or pastes, or may be foams, with tinygas bubbles suspended in a liquid. As used herein, the term “emulsion”encompasses continuous phases comprising gas bubbles, continuous phasescomprising particles (e.g., solid catalyst), continuous phasescomprising droplets of a fluid that is substantially insoluble in thecontinuous phase, and combinations thereof.

Feed stream 205 may include a particulate solid catalyst component. Feedstream 205 is pumped through the generators 220, 230, 240, such thatproduct dispersion 210 is formed. In each generator, the rotors 222,223, 224 rotate at high speed relative to the fixed stators 227, 228,229. The rotation of the rotors pumps fluid, such as the feed stream205, between the outer surface of the rotor 222 and the inner surface ofthe stator 227 creating a localized high shear condition. The gaps 225,235, 245 generate high shear forces that process the feed stream 205.The high shear forces between the rotor and stator functions to processthe feed stream 205 to create the product dispersion 210. Each generator220, 230, 240 of the high shear device 200 has interchangeablerotor-stator combinations for producing a narrow distribution of thedesired bubble size, if feedstream 205 comprises a gas, or globule size,if feedstream 205 comprises a liquid, in the product dispersion 210.

The product dispersion 210 of gas particles, or bubbles, in a liquidcomprises an emulsion. In embodiments, the product dispersion 210 maycomprise a dispersion of a previously immiscible or insoluble gas,liquid or solid into the continuous phase. The product dispersion 210has an average gas particle, or bubble, size less than about 1.5 μm;preferably the bubbles are sub-micron in diameter. In certain instances,the average bubble size is in the range from about 1.0 μm to about 0.1μm. Alternatively, the average bubble size is less than about 400 nm(0.4 μm) and most preferably less than about 100 nm (0.1 μm).

The high shear device 200 produces a gas emulsion capable of remainingdispersed at atmospheric pressure for at least about 15 minutes. For thepurpose of this disclosure, an emulsion of gas particles, or bubbles, inthe dispersed phase in product dispersion 210 that are less than 1.5 μmin diameter may comprise a micro-foam. Not to be limited by a specifictheory, it is known in emulsion chemistry that sub-micron particles, orbubbles, dispersed in a liquid undergo movement primarily throughBrownian motion effects. The bubbles in the emulsion of productdispersion 210 created by the high shear device 200 may have greatermobility through boundary layers of solid catalyst particles, therebyfacilitating and accelerating the catalytic reaction through enhancedtransport of reactants.

The rotor is set to rotate at a speed commensurate with the diameter ofthe rotor and the desired tip speed as described hereinabove. Transportresistance is reduced by incorporation of high shear device 200 suchthat the velocity of the reaction is increased by at least about 5%.Alternatively, the high shear device 200 comprises a high shear colloidmill that serves as an accelerated rate reactor (ARR). The acceleratedrate reactor comprises a single stage dispersing chamber. Theaccelerated rate reactor comprises a multiple stage inline dispersercomprising at least 2 stages.

Selection of the high shear device 200 is dependent on throughputrequirements and desired particle or bubble size in the outletdispersion 210. In certain instances, high shear device 200 comprises aDispax Reactor® of IKA® Works, Inc., Wilmington, N.C. and APV NorthAmerica, Inc., Wilmington, Mass. Model DR 2000/4, for example, comprisesa belt drive, 4M generator, PTFE sealing ring, inlet flange 1″ sanitaryclamp, outlet flange ¾″ sanitary clamp, 2 HP power, output speed of 7900rpm, flow capacity (water) approximately 300 l/h to approximately 700l/h (depending on generator), a tip speed of from 9.4 m/s to about 41m/s (about 1850 ft/min to about 8070 ft/min). Several alternative modelsare available having various inlet/outlet connections, horsepower,nominal tip speeds, output rpm, and nominal flow rate.

Without wishing to be limited to a particular theory, it is believedthat the level or degree of high shear is sufficient to increase ratesof mass transfer and may also produce localized non-ideal conditionsthat enable reactions to occur that would not otherwise be expected tooccur based on Gibbs free energy predictions. Localized non idealconditions are believed to occur within the high shear device resultingin increased temperatures and pressures with the most significantincrease believed to be in localized pressures. The increase inpressures and temperatures within the high shear device areinstantaneous and localized and quickly revert back to bulk or averagesystem conditions once exiting the high shear device. In some cases, thehigh shear device induces cavitation of sufficient intensity todissociate one or more of the reactants into free radicals, which mayintensify a chemical reaction or allow a reaction to take place at lessstringent conditions than might otherwise be required. Cavitation mayalso increase rates of transport processes by producing local turbulenceand liquid micro-circulation (acoustic streaming).

Vessel. Vessel or reactor 110 is any type of vessel in which amultiphase reaction can be propagated to carry out the above-describedconversion reaction(s). For instance, a continuous or semi-continuousstirred tank reactor, or one or more batch reactors may be employed inseries or in parallel. In some applications vessel 110 may be a towerreactor, and in others a tubular reactor or multi-tubular reactor. Acatalyst inlet line 115 may be connected to vessel 110 for receiving acatalyst solution or slurry during operation of the system.

Vessel 110 may include one or more of the following components: stirringsystem, heating and/or cooling capabilities, pressure measurementinstrumentation, temperature measurement instrumentation, one or moreinjection points, and level regulator (not shown), as are known in theart of reaction vessel design. For example, a stirring system mayinclude a motor driven mixer. A heating and/or cooling apparatus maycomprise, for example, a heat exchanger. Alternatively, as much of theconversion reaction may occur within HSD 140 in some embodiments, vessel110 may serve primarily as a storage vessel in some cases. Althoughgenerally less desired, in some applications vessel 110 may be omitted,particularly if multiple high shears/reactors are employed in series, asfurther described below.

Heat Transfer Devices. In addition to the above-mentionedheating/cooling capabilities of vessel 110, other external or internalheat transfer devices for heating or cooling a process stream are alsocontemplated in variations of the embodiments illustrated in FIG. 1.Some suitable locations for one or more such heat transfer devices arebetween pump 105 and HSD 140, between HSD 140 and vessel 110, andbetween vessel 110 and pump 105 when system 1 is operated in multi-passmode. Some non-limiting examples of such heat transfer devices areshell, tube, plate, and coil heat exchangers, as are known in the art.

Pumps. Pump 105 is configured for either continuous or semi-continuousoperation, and may be any suitable pumping device that is capable ofproviding greater than 2 atm pressure, preferably greater than 3 atmpressure, to allow controlled flow through HSD 140 and system 1. Forexample, a Roper Type 1 gear pump, Roper Pump Company (Commerce, Ga.)Dayton Pressure Booster Pump Model 2P372E, Dayton Electric Co. (Niles,Ill.) is one suitable pump. Preferably, all contact parts of the pumpcomprise stainless steel. In some embodiments of the system, pump 105 iscapable of pressures greater than about 20 atm. In addition to pump 105,one or more additional, high pressure pump (not shown) may be includedin the system illustrated in FIG. 1. For example, a booster pump, whichmay be similar to pump 105, may be included between HSD 140 and vessel110 for boosting the pressure into vessel 110. As another example, asupplemental feed pump, which may be similar to pump 105, may beincluded for introducing additional reactants or catalyst into vessel110.

Hydration of Alkylene oxides. In operation for the catalytic hydrationof alkylene oxides, respectively, a dispersible alkylene oxide gasstream is introduced into system 100 via line 122, and combined in line113 with a water stream to form a gas-liquid stream. Alternatively, thealkylene oxide gas may be fed directly into HSD 140, instead of beingcombined with the liquid reactant (i.e., water) in line 113. Pump 105 isoperated to pump the liquid reactant (water) through line 121, and tobuild pressure and feed HSD 140, providing a controlled flow throughouthigh shear (HSD) 140 and high shear system 100.

In a preferred embodiment, alkylene oxide gas may continuously be fedinto the water stream 112 to form high shear feed stream 113 (e.g. agas-liquid stream). In high shear device 140, water and the alkyleneoxide vapor are highly dispersed such that nanobubbles and/ormicrobubbles of alkylene oxide are formed for superior dissolution ofalkylene oxide vapor into solution. Once dispersed, the dispersion mayexit high shear device 140 at high shear outlet line 118. Stream 118 mayoptionally enter fluidized or fixed bed 142 in lieu of a slurry catalystprocess. However, in a slurry catalyst embodiment, high shear outletstream 118 may directly enter hydration reactor 110 for hydration. Thereaction stream may be maintained at the specified reaction temperature,using cooling coils in the reactor 110 to maintain reaction temperature.Hydration products (e.g. alkylene glycols) may be withdrawn at productstream 116.

In an exemplary embodiment, the high shear device comprises a commercialdisperser such as IKA® model DR 2000/4, a high shear, three stagedispersing device configured with three rotors in combination withstators, aligned in series. The disperser is used to create thedispersion of alkylene oxides in the liquid medium comprising water(i.e., “the reactants”). The rotor/stator sets may be configured asillustrated in FIG. 2, for example The combined reactants enter the highshear device via line 113 and enter a first stage rotor/statorcombination having circumferentially spaced first stage shear openings.The coarse dispersion exiting the first stage enters the secondrotor/stator stage, which has second stage shear openings. The reducedbubble-size dispersion emerging from the second stage enters the thirdstage rotor/stator combination having third stage shear openings. Thedispersion exits the high shear device via line 118. In someembodiments, the shear rate increases stepwise longitudinally along thedirection of the flow. For example, in some embodiments, the shear ratein the first rotor/stator stage is greater than the shear rate insubsequent stage(s). In other embodiments, the shear rate issubstantially constant along the direction of the flow, with the stageor stages being the same. If the high shear device includes a PTFE seal,for example, the seal may be cooled using any suitable technique that isknown in the art. For example, the reactant stream flowing in line 113may be used to cool the seal and in so doing be preheated as desiredprior to entering the high shear device.

The rotor of HSD 140 is set to rotate at a speed commensurate with thediameter of the rotor and the desired tip speed. As described above, thehigh shear device (e.g., colloid mill) has either a fixed clearancebetween the stator and rotor or has adjustable clearance. HSD 140 servesto intimately mix the alkylene oxide vapor and the reactant liquid(i.e., water). In some embodiments of the process, the transportresistance of the reactants is reduced by operation of the high sheardevice such that the velocity of the reaction (i.e. reaction rate) isincreased by greater than a factor of about 5. In some embodiments, thevelocity of the reaction is increased by at least a factor of 10. Insome embodiments, the velocity is increased by a factor in the range ofabout 10 to about 100 fold. In some embodiments, HSD 140 delivers atleast 300 L/h with a power consumption of 1.5 kW at a nominal tip speedof at least 4500 ft/min, and which may exceed 7900 ft/min (140 m/sec).Although measurement of instantaneous temperature and pressure at thetip of a rotating shear unit or revolving element in HSD 140 isdifficult, it is estimated that the localized temperature seen by theintimately mixed reactants may be in excess of 500° C. and at pressuresin excess of 500 kg/cm² under high shear conditions. The high shearresults in dispersion of the alkylene oxide gas in micron orsubmicron-sized bubbles. In some embodiments, the resultant dispersionhas an average bubble size less than about 1.5 μm. Accordingly, thedispersion exiting HSD 140 via line 118 comprises micron and/orsubmicron-sized gas bubbles. In some embodiments, the mean bubble sizeis in the range of about 0.4 μm to about 1.5 μm. In some embodiments,the mean bubble size is less than about 400 nm, and may be about 100 nmin some cases. In many embodiments, the microbubble dispersion is ableto remain dispersed at atmospheric pressure for at least 15 minutes.

Once dispersed, the resulting alkylene oxide/water dispersion exits HSD140 via line 118 and feeds into vessel 110, as illustrated in FIG. 1. Asa result of the intimate mixing of the reactants prior to enteringvessel 110, a significant portion of the chemical reaction may takeplace in HSD 140, with or without the presence of a catalyst.Accordingly, in some embodiments, reactor/vessel 110 may be usedprimarily for heating and separation of volatile reaction products fromthe alkylene glycol product. Alternatively, or additionally, vessel 110may serve as a primary reaction vessel where most of the alkylene glycolproduct is produced. Vessel/reactor 110 may be operated in eithercontinuous or semi-continuous flow mode, or it may be operated in batchmode. The contents of vessel 110 may be maintained at a specifiedreaction temperature using heating and/or cooling capabilities (e.g.,cooling coils) and temperature measurement instrumentation. Pressure inthe vessel may be monitored using suitable pressure measurementinstrumentation, and the level of reactants in the vessel may becontrolled using a level regulator (not shown), employing techniquesthat are known to those of skill in the art. The contents are stirredcontinuously or semi-continuously.

Commonly known hydration reaction conditions may suitably be employed asthe conditions of the production of an alkylene glycol by hydratingalkylene oxides by using catalysts. There is no particular restrictionas to the reaction conditions. For exemplary purposes, the method willbe discussed with respect to ethylene glycol. However, it is envisionedthat embodiments of the method may be used to produce any alkyleneglycol. In the production of ethylene glycol, theoretically one mole ofwater is required to hydrate one mole of ethylene oxide. Actually,however, greater than equal molecular proportions of water to ethyleneoxide are required for good results. Although a conversion ofapproximately 90% can sometimes be obtained when employing a reactantratio of water to ethylene oxide of around 2, reactant ratios of greaterthan 6 are generally required to achieve reasonably high yields ofproducts, otherwise the ethylene glycol formed reacts with ethyleneoxide to form di- and triethylene glycols. The effects of the reactantratios on the results obtained for the production of ethylene glycol andother alkylene glycols are well known. In reacting steam and ethyleneoxide in a ratio of at least 17:1 over a stationary bed of the claimedcatalyst, yields based on the ethylene oxide consumed are found to bereasonably high.

The primary by-products of the hydrolysis reaction are di- andpolyglycols, e.g., dialkylene glycol, trialkylene glycol andtetra-alkylene glycol. The formation of the di- and polyglycols isbelieved to be primarily due to the reaction of alkylene oxide withalkylene glycol. As alkylene oxides are generally more reactive withalkylene glycols than they are with water, large excesses of water areemployed in order to favor the reaction with water and thereby obtain acommercially-attractive selectivity to the monoglycol product.

The reaction temperature, which varies depending upon the type of thestarting alkylene oxide, the type of the catalyst, the composition ofthe reactant mixture at the early stage of the reaction, etc., isgenerally 50° C. to 200° C., preferably 110° C. to 160° C. The reactionpressure, which varies according to the amount of carbon dioxide, thereaction temperature, and the extent of advance of the reaction, isgenerally 3 to 50 kg/cm². If desired, the pressure within the reactormay be adjusted occasionally. The reaction time may be about 30 minutesto about 3 hours. The contacting time of the reactants over a catalystcan vary anywhere from period of less than a second to periods rangingup to 25 seconds.

The alkylene oxides for the reaction may be used alone or in combinationas a mixture of different types. The alkylene oxides can have anystructure, such as, aliphatic, aromatic, heteroaromatic,aliphatic-aromatic or aliphatic-heteroaromatic. They can also containother functional groups, and it should be determined beforehand whetherthese functional groups should remain unchanged or should be hydratedthemselves.

Embodiments of the disclosed process may be suitable for hydratingstraight or branched alkylene oxides. Example of alkylene oxides includewithout limitation, ethylene oxide, butylenes oxide, propylene oxide,and the like. The alkylene oxide may have from 2 to 4 carbon atoms.

Catalyst. If a catalyst is used to promote the hydration reaction, itmay be introduced into the vessel via line 115, as an aqueous ornonaqueous slurry or stream. Alternatively, or additionally, catalystmay be added elsewhere in the system 100. For example, catalyst slurrymay be injected into line 121. In some embodiments, line 121 may containa flowing water stream and/or alkylene oxide recycle stream from vessel110.

In embodiments, any catalyst suitable for catalyzing a hydrationreaction may be employed. An inert gas such as nitrogen may be used tofill reactor 110 and purge it of any air and/or oxygen. According to oneembodiment, the catalysts useful in the disclosed process may be acidcatalysts. For example, partially amine-neutralized sulfonic acidcatalysts may be used as the catalyst. These catalysts are heterogeneousand may be described more completely as sulfonic acid-type ion exchangeresins. These resins are then modified by passing sufficient aminethrough the resin to partially neutralize the sulfonic acid groupscontained therein. Primary, secondary or tertiary amines are eachacceptable. Tertiary amines may be used in the disclosed process. Theresult is a catalyst which consists of a mixture of the original freesulfonic acid and the amine salt of the sulfonic acid, all still in theheterogeneous form.

In a specific embodiment, catalyst comprises a styrene-divinylbenzenecopolymer matrix with pendant sulfonic acid groups. Catalysts fallingwithin this species are available from Rohm and Haas under thedesignation Amberlyst RTM 15 and Amberlyst XN-1010 which differ in theamount of surface area available. Other matrices than thestyrene-divinylbenzene type could be used, including other organicpolymers and inorganic materials, provided only that the substrate becapable of binding the sulfonic acid groups to maintain a heterogeneouscatalyst system.

Other representatives of the numerous acid catalysts that have beensuggested for use in the hydration of alkylene oxides includefluorinated alkyl sulfonic acid ion exchange resins, carboxylic acidsand halogen acids, strong acid cation exchange resins, aliphatic mono-and/or polycarboxylic acids, cationic exchange resins, acidic zeolites,sulfur dioxide, trihalogen acetic acids.

In addition to the acid catalysts, numerous catalysts have beensuggested for the hydration of alkylene oxides. For example, thecatalyst may be an aluminum phosphate catalyst, organic tertiary aminessuch as triethylamine and pyridine, quarternary phosphonium salts,fluoroalkyl sulfonic acid resins, alkali metal halides such aschlorides, bromides and iodides of potassium, sodium and lithium, orquaternary ammonium halides such as tetramethylammonium iodide andtetraethylammonium bromide, or combinations thereof.

Various metal-containing compounds, including metal oxides, may be usedas catalysts for the hydrolysis of alkylene oxides. For example, adehydrating metal oxide such as without limitation, alumina, thoria, oroxides or tungsten, titanium, vanadium, molybdenum or zirconium. Oralternatively alkali metal bases may be used such as alkyleneglycolates, oxides of titanium, tungsten and thorium.

The catalyst may also comprise an organometallic compounds includingmetals such as vanadium, molybdenum, tungsten, titantium, chromium,zirconium, selenium, tellurium, tantalum, rhenium, uranium, orcombinations thereof.

More recently, U.S. Pat. No. 4,277,632, issued Jul. 7, 1981, discloses aprocess for the production of alkylene glycols by the hydrolysis ofalkylene oxides in the presence of a catalyst of at least one memberselected from the group consisting of molybdenum and tungsten. Catalystmay be fed into reactor 110 through catalyst feed stream 115.Alternatively, catalyst may be present in a fixed or fluidized bed 142.

The bulk or global operating temperature of the reactants is desirablymaintained below their flash points. In some embodiments, the operatingconditions of system 100 comprise a temperature in the range of fromabout 50° C. to about 300° C. In specific embodiments, the reactiontemperature in vessel 110, in particular, is in the range of from about90° C. to about 220° C. In some embodiments, the reaction pressure invessel 110 is in the range of from about 5 atm to about 50 atm.

The dispersion may be further processed prior to entering vessel 110 (asindicated by arrow 18), if desired. In vessel 110, alkylene oxidehydration occurs via catalytic hydration. The contents of the vessel arestirred continuously or semi-continuously, the temperature of thereactants is controlled (e.g., using a heat exchanger), and the fluidlevel inside vessel 110 is regulated using standard techniques. Alkyleneoxide hydration may occur either continuously, semi-continuously orbatch wise, as desired for a particular application. Any reaction gasthat is produced exits reactor 110 via gas line 117. This gas stream maycomprise unreacted alkylene oxides, for example. The reaction gasremoved via line 117 may be further treated, and the components may berecycled, as desired.

The reaction product stream including unconverted alkylene oxides andcorresponding byproducts exits (e.g. di- and polyglycols, dialkyleneglycol, trialkylene glycol and tetra-alkylene glycol) vessel 110 by wayof line 116. The alkylene glycol product may be recovered and treated asknown to those of skill in the art.

Multiple Pass Operation. In the embodiment shown in FIG. 1, the systemis configured for single pass operation, wherein the output from vessel110 goes directly to further processing for recovery of alkylene glycolproduct. In some embodiments it may be desirable to pass the contents ofvessel 110, or a liquid fraction containing unreacted alkylene oxide,through HSD 140 during a second pass. In this case, line 117 isconnected to line 121 via dotted line 120, and the recycle stream fromvessel 110 is pumped by pump 105 into line 113 and thence into HSD 140.Additional alkylene oxide gas may be injected via line 122 into line113, or it may be added directly into the high shear device (not shown).

Multiple High Shear Devices. In some embodiments, two or more high sheardevices like HSD 140, or configured differently, are aligned in series,and are used to further enhance the reaction. Their operation may be ineither batch or continuous mode. In some instances in which a singlepass or “once through” process is desired, the use of multiple highshear devices in series may also be advantageous. In some embodimentswhere multiple high shear devices are operated in series, vessel 110 maybe omitted. In some embodiments, multiple high shear devices 140 areoperated in parallel, and the outlet dispersions therefrom areintroduced into one or more vessel 110.

While embodiments of the invention have been shown and described,modifications thereof can be made by one skilled in the art withoutdeparting from the spirit and teachings of the invention. Theembodiments described herein are exemplary only, and are not intended tobe limiting. Many variations and modifications of the inventiondisclosed herein are possible and are within the scope of the invention.Where numerical ranges or limitations are expressly stated, such expressranges or limitations should be understood to include iterative rangesor limitations of like magnitude falling within the expressly statedranges or limitations. Use of broader terms such as comprises, includes,having, etc. should be understood to provide support for narrower termssuch as consisting of, consisting essentially of, comprisedsubstantially of, and the like. Accordingly, the scope of protection isnot limited by the description set out above but is only limited by theclaims which follow, that scope including all equivalents of the subjectmatter of the claims. Each and every original claim is incorporated intothe specification as an embodiment of the invention. Thus, the claimsare a further description and are an addition to the preferredembodiments of the present invention. The disclosures of all patents,patent applications, and publications cited herein are herebyincorporated by reference, to the extent they provide exemplary,procedural or other details supplementary to those set forth herein.

1. A method of hydrating an alkylene oxide comprising: a) emulsifying analkylene oxide gas in a water stream in a high shear device under highshear conditions to produce a dispersion comprising gas bubbles having amean diameter of less than about 1 micron; and b) contacting thedispersion with a catalyst to hydrate the alkylene oxide gas and form analkylene glycol.
 2. The method of claim 1 wherein said high shearconditions comprise local temperatures and local pressures that aresubstantially higher than bulk temperature and bulk pressure in the highshear device.
 3. The method of claim 1, wherein the gas bubbles have anaverage diameter of no more than about 400 nm.
 4. The method of claim 1,wherein the alkylene oxide gas is selected from the group consisting ofethylene oxide, propylene oxide, butylene oxide, and combinationsthereof.
 5. The method of claim 1, wherein the water stream includes aliquid-gas stream formed by mixing a second alkylene oxide gas streamwith water.
 6. The method of claim 1, wherein (a) comprises subjectingsaid alkylene oxide gas and water to high shear mixing at a tip speed ofat least about 23 m/sec.
 7. The method of claim 1, wherein (a) comprisessubjecting said alkylene oxide gas and water to a shear rate of greaterthan about 20,000 s⁻¹.
 8. The method of claim 1, wherein the catalyst isselected from the group consisting of amines, acid catalysts,organometallic compounds, alkali metal halides, quaternary ammoniumhalides, zeolites, and combinations thereof.
 9. The method of claim 1,wherein the alkylene glycol comprises ethylene glycol.
 10. A method ofhydrating an alkylene oxide comprising: a) forming a dispersion of analkylene oxide gas and a water stream in a high shear device under highshear conditions, wherein said dispersion comprises gas bubbles having amean diameter of less than about 1 micron; and b) introducing saiddispersion into a fixed-bed reactor to hydrate the alkylene oxide gasand form an alkylene glycol, wherein said fixed-bed reactor comprises ahydration catalyst.
 11. The method of claim 10, wherein forming saiddispersion comprises an energy expenditure of at least about 1000 W/m³.12. The method of claim 10, wherein the hydration catalyst is selectedfrom the group consisting of amines, acid catalysts, organometalliccompounds, alkali metal halides, quaternary ammonium halides, zeolites,and combinations thereof.
 13. The method of claim 10, wherein thealkylene glycol comprises ethylene glycol.
 14. The method of claim 10,wherein the high shear device comprises two or more rotors and two ormore stators.
 15. A method of hydrating an alkylene oxide comprising: a)forming a dispersion of an alkylene oxide gas and a water stream in ahigh shear device comprising a generator under high shear conditions,wherein said dispersion comprises gas bubbles having a mean diameter ofless than about 1 micron; and b) introducing said dispersion into avessel; and c) introducing a catalyst slurry comprising a hydrationcatalyst into said vessel and allowing hydration of the alkylene oxidegas to take place and to produce an alkylene glycol.
 16. The method ofclaim 15 further comprising mixing a hydration catalyst with the waterstream.
 17. The method of claim 15, wherein said high shear devicecomprises a rotor and a stator separated by a shear gap in the range offrom about 0.02 mm to about 5 mm, wherein the shear gap is a minimumdistance between said rotor and said stator.
 18. The method of claim 15comprising utilizing more than one generator.
 19. The method of claim 15further comprising utilizing at least two high shear devices.
 20. Themethod of claim 19, wherein the shear rate provided by one of the atleast two high shear devices is greater than the shear rate provided byanother of the at least two high shear devices.